At once their lines began edging sideways, towards the western harbour. It was only a short distance, but they could not let down their guard at all. Seeing this attempt to escape, the Nubians yelled with anger and sprang forward again.

'Keep going,' cried the centurion nearest Romulus. 'Stop just before they hit. Stay in formation and drive them back. Then move on.'

Romulus eyed the triremes, which numbered about twenty. There would be room on board for all – but where would they go?

As ever, Tarquinius butted in with the answer. 'To the Pharos.' He pointed at the lighthouse. 'Over there, the Heptastadion is only fifty or sixty paces across.'

His confidence restored, Romulus grinned. 'We can defend that until doomsday.'

Yet the ships were still out of reach and, a heartbeat later, the Nubians struck the Roman formation with such force that the front ranks were driven back several steps. Screams filled the night air and soldiers cursed the bad luck sent them by the gods. Romulus saw a legionary to his left take a spear through one calf and go down thrashing. Horrendously, another had a blade pierce both cheeks to emerge on the other side of his face. Blood jetted from the wounds as the weapon was withdrawn. Dropping his scutum and sword, the soldier raised both hands to his ruined face and let out a thin, piercing cry. Romulus lost sight of both injured men as a mass of Nubians slammed up against his section.

Angry red mouths shouted insults in a foreign tongue. Hide shields smacked off scuta and broad spear blades flickered back and forth, searching for Roman flesh. Romulus' nostrils were filled with the black warriors' musty body odour. Quickly he killed the first man within reach, sliding his gladius under the man's sternum in one easy move. His next opponent was no harder to despatch; he practically ran on to Romulus' sword. The Nubian was dead before he'd even realised it.

On Romulus' right, Tarquinius was also dispatching warriors with ease, but to his left, the talkative legionary was struggling. Beset by two hulking Nubians, he soon took a spear through his right shoulder, which crippled him. He had no chance as one of his enemies pulled down his shield while the other stabbed him through the throat. It was the last thing the first Nubian did. Romulus lopped off his right hand, the one holding the spear, and with the backstroke opened the warrior's flesh from his groin to his shoulder. A legionary from the rank behind moved forward to fill the gap and together they killed the second warrior.

The dead were replaced immediately.

We need cavalry, thought Romulus as he fought on. Or some catapults. A different tactic to help their cause, which was growing desperate. Small numbers of legionaries had reached the triremes and were swarming aboard, but the majority remained trapped in a fight which they could not win. Panic flared in men's hearts and instinctively they moved backwards. Centurions roared at them to stand fast, and the standard-bearers shook their poles, trying to restore confidence, but it was no good. More ground was given away. Scenting blood, the enemy redoubled their efforts.

Romulus did not like it. He could see the situation unravelling fast.

'Keep moving!' cried a voice from behind him. 'Hold your formation. Take heart, comrades. Caesar is here!'

Romulus risked a look over his shoulder.

A lithe figure in gilded breastplate and red general's cloak was pushing through to join them. His horsehair-crested helmet was especially well wrought, with silver and gold filigree worked into the cheek pieces. Caesar was carrying a gladius with an ornate ivory hilt and an ordinary scutum. Romulus took in a narrow face with high cheekbones, an aquiline nose and piercing, dark eyes. Caesar's features reminded him of someone, but he had no time to dwell on the thought. He took heart from Caesar's calm manner, however. Like the centurions, he was prepared to put his life on the line, and where a leader like Caesar stood, soldiers would not run.

Struck, Tarquinius looked from the general to Romulus and back again.

Romulus was oblivious.

The news rippled through the ranks. At once the atmosphere changed, the panic dissipating like early morning mist. Disobeying orders, the re-invigorated legionaries surged forward again, catching the enemy unawares. Soon the lost ground had been regained, and there was a brief respite. With the ground between the lines littered with bloody bodies, writhing casualties and discarded weapons, both sides stood watching each other warily. Clouds of breaths steamed the air and sweat ran freely from the felt liners under bronze helmets.

It was Caesar's moment.

'Remember our battle against the Nervii, comrades?' he asked loudly. 'We won then, eh?'

The legionaries roared with approval. Their victory against the valiant tribe had been one of the hardest fought in the entire Gaulish campaign.

'And Alesia?' Caesar went on. 'The Gauls were swarming over us like clouds of flies there. But we still beat them!'

Another shout went up.

'Even at Pharsalus, when no one gave us a chance in Hades,' Caesar said dramatically, encompassing them all with his arms, 'you, my comrades, gained victory.'

Romulus saw real pride appear in men's faces; he felt their resolve stiffen. Caesar was one of them. A soldier. Romulus felt his own respect growing. This was a remarkable leader.

'Cae-sar!' bellowed a grizzled veteran. 'Cae-sar!'

Everyone took up the cry, including Romulus.

Even Tarquinius joined in.

Caesar let his men cheer for a moment, and then began urging them towards the triremes once more.

They nearly made it. Intimidated by the Romans' counter-attack and Caesar's bold words, the Egyptian troops held back for twenty heartbeats. Soon the edge of the dock was only a stone's throw away. Guided by sailors, hundreds more legionaries had embarked, and a good number of the low-slung ships had pushed out into the harbour. The three banks of oars on each dug down, pulling them into deeper water. Finally, furious that their foes were escaping, the enemy officers acted. Exhorting their men to finish what had been started, they charged forward, followed quickly by a roiling mass of soldiers that threatened only one thing. Annihilation.

'Spread out!' Caesar ordered. 'Form a line in front of the triremes.'

His men hurried to obey.

It was all too slow, thought Romulus with a thrill of dread. Manoeuvres like this could not be done properly with an enemy host closing in from thirty paces away.

Tarquinius' gaze lifted to the starlit sky, searching for a sign. Where was the wind coming from? Was it about to change? He needed to know, but he was afforded no time.

An instant later, the Egyptians reached them. Attacking a force on the point of retreat was one of the best ways to win a battle, and they sensed it instinctively. Spears reached out, delivering the bloody kiss of death to legionaries who were turning to run. Gladii wielded by Gabinius' former soldiers stabbed through weakened links of mail, or into vulnerable armpits; they hammered the shields from their hands. Bronze helmets were smashed into bent pieces of metal and men's skulls cracked open. Humming overhead came sheets of arrows and showers of stones. Seeing the lethal pieces of rock, Romulus' heart sank. With enemy slingers in range, their casualties would soar.

Fear now distorted most legionaries' faces. Others threw terrified glances at the heavens and prayed aloud. Caesar's rallying shouts were in vain. There simply weren't enough of them to hold the Egyptians back. The fight became a frantic effort not to fold completely. Still Romulus hacked and slashed, holding his own. With an agility belying his years, Tarquinius was doing the same. The soldier who had joined Romulus on his left side was a skilled fighter too. Together they made a fearsome trio – yet it made little difference to the greater situation.